This invention relates generally to ceramic insulators and more particularly to a composition for coating such insulators in order to improve their anti-arcing capability.
Ceramic components intended for high voltage insulator service must be virtually moisture free in order to preclude failure due to arcing or flashover. A standard practice for removing moisture from ceramic insulators is to bake the insulators at elevated temperatures under vacuum conditions. While still under vacuum, an anti-arcing coating is applied to the insulator. Such anti-arcing compounds usually consist of an acrylic polymer dissolved in a solvent, several varieties of which are commercially available.
Many ceramics are, however, temperature or pressure sensitive. High temperature baking under vacuum is not feasible for removing traces of moisture from such ceramics. Furthermore, drying under vacuum below the ceramic's temperature limit has proven insufficient when high voltage service is intended. It appears that residual water from the ceramic crystals diffuses into the anti-arcing coating and causes failure of the coating interface at high voltage conditions.
Additionally, most anti-arcing coatings are rather brittle and thus do not have good impact resistance. Furthermore, there is presently no effective means for readily determining the presence of large amounts of residual moisture in the ceramic component.